Battery Monitor

Gtboosted

New member
I am trying to see what type of battery monitor do I need. My trailer did not come with one and I hate the guessing game when I am out there.

Also, do I need a basic one or is it worth the cost and installation for something that can tell me how much current my fridge is pulling for example.

Here is what I have
Guest 6amp on board charger
Lifeline 100ah AGM deep cycle battery
Renogy Solar Suitcase 100w
ARB 50 Fridge
12v water pump
Stereo with 2 speakers
Interior and exterior LED lights
4x 12v ports

If I do get a basic one, are the readings reliable? For example, past trip the kids wanted to charge a few devices but after not using solar during the day I wasn't sure how much battery I had left so I told them no. If I had a battery monitor I could trust it would've be an easy decision.
 

Buddha.

Lurker
I had the Victron 712 in my last rig and it was fine but I also wonder if there’s a cheaper option. I certainly didn’t use all of the features of the Victron.
 

2.ooohhh

Member
I use CTEK sense modules to monitor vehicles parked more than driven, the wife’s car, and trailers. Pings my phone as I walk by if battery needs charge/attention.


Sent from my iPhone using Tapatalk
 

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john61ct

Adventurer
The Victron BMV is a good unit, extra features, pretty accurate for a shunt based coulomb counter, yes pricey, includes amps and Ah along with SoC% and V, works with both LFP and lead.

Hard to install and harder to keep (sort of) accurate.

Xantrex Link 2000 similar, bit more accurate, personally hate the company's CS attitude


Merlin Smartgauge, from Balmar in the new world is the most accurate, easiest to install, less updating required, but lead banks only, and SoC% and V only, not shunt based so no amps/Ah counting. Cheaper to order from the UK usually.

Do **not** buy Balmar's SG-200, still alpha stage IMO.

A wattmeter to count coulombs is very inaccurate, not really a proper monitor, but cheap.

Same with this, looks nicer but. . .

HENGSHAN AiLi Battery Monitor Voltmeter Ammeter Voltage Current Meter 8-80V 0-100A Auto Car Motor Boat Caravan RV Motorhome
 

Rando

Explorer
If you don't mind not having a physical display, the Victron smart shunt gives you all the functionality of the Victron BMV series but you can only view on your smart phone. It saves you about $70:
 

jonyjoe101

Adventurer
tk15 is what I use, I recommend to everyone. The 50a version is about 30 dollars. Its bidirectional counts amps in/out of the battery. With this you will know exactly how much amps your fridge is using. You only have to program your battery AH rating and the battery full voltage and depleted voltage (14.4 volts and 11.5 volts for lead acid). When the meter reads 50 percent, the battery voltage should be around 12.1 volts.

tk15
tk15 couloumb.jpg

This is the tk15 being tested with a dc wattmeter, both readings are almost the same. Its good enough for me.
a coulometer.jpg
 

Gtboosted

New member
Thanks everyone. I read thru all the suggestions. I went with the Merlin Smartgauge due to it's simple install. Also read a few articles and it was always praised.

Found one on ebay for $90 so it was a no brainer.
 

vomhorizon

Active member
If you don't mind not having a physical display, the Victron smart shunt gives you all the functionality of the Victron BMV series but you can only view on your smart phone. It saves you about $70:
Been using it for a couple of months and love the functionality and the app is pretty intuitive.
 

john61ct

Adventurer
Found one on ebay for $90 so it was a no brainer.
Fantastic deal!

Make sure to get the full documentation, follow the (easy) install details exactly. e.g using #14 AWG wire only is critical


 

Martinjmpr

Wiffleball Batter
You know, I was just about to post a question about how battery monitors work. All I have on my battery box is a voltage reading. I know a voltage reading can give you a so-so guess on SoC but I'd like to be able to incorporate a true battery monitor so I would now what % of power I had used or better yet, how many AH I had used and how many I had available.

EDIT: So I just did some Amazon searching and came across quite a few "battery monitors." Am I right in thinking that most of these cheap "battery monitors" are simply voltage meters that equate a given voltage with a given State of Charge (SoC?) So for example, if a 12v lead acid battery is reading, say, 12.2v it will show a "50% charge" or something like that? And am I correct that the more complex and expensive ones are actually coulomb meters that can measure the actual energy usage? I'd like to be able to employ something like this, both for my power box and also for our trailer, so I can know the actual state of charge and how much power I'm getting from the solar panel but I'm a bit confused about which item is just a cheap volt meter vs. something more accurate.
 
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john61ct

Adventurer
You know, I was just about to post a question about how battery monitors work.
There is no one way. Voltage is pretty useless, super inaccurate.

A shunt counting Ah more common and much better, but read the Victron BMV manual closely plus these



Best that type gets is maybe 10% accuracy, and that is only when properly installed, with

frequent 100% Full resets

Peukert value and CEF settings and

kept-accurate Ah capacity as it declines

maintained.

______
Then you have Merlin SmartGauge, requires none of that, much better accuracy, say 3-6% when at rest or low currents flowing.

But does not show this directly:

> how many AH I had used and how many I had available.

only SoC and voltage (for the two batteries)

> EDIT: So I just did some Amazon searching and came across quite a few "battery monitors." Am I right in thinking that most of these cheap "battery monitors" are simply voltage meters that equate a given voltage with a given State of Charge (SoC?)

maybe, but more likely count coulombs / Ah

but cheap ones do not compensate for Peukert value, no CEF, not accurate, at all
 

67cj5

Man On a Mission
You don't need any of these expensive models, You can get one from Amazon that you just put on your battery terminals and it Bluetooths to your phone with an App, and costs about 25 / 30 bucks, ?
 

john61ct

Adventurer
I would not count those as proper "battery monitor"

really just a coulomb-counting wattmeter.

Yes they work "fine" if you don't care about accuracy, can be as much as 20-30% off.
 

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67cj5

Man On a Mission
I would not count those as proper "battery monitor"

really just a coulomb-counting wattmeter.

Yes they work "fine" if you don't care about accuracy, can be as much as 20-30% off.
Like all these gizmo's we buy they should be tested or calibrated before hand if possible, and even if they are out as long as you know the offset then you can allow for that.
 

john61ct

Adventurer
Calibrating against what yardstick?

The whole point is there is no way to get (reasonably) accurate SoC between the extreme ends

other than an accurate-as-possible battery monitor.

If your only tools are something less accurate, there is no way to calibrate them.

Again, a basic wattmeter is "fine" if you only want rough numbers

and reset at accurately measured 100% Full each cycle via endAmps.

Personally, taking the family out to a restaurant meal cost as much or more than a SmartGauge

so if I skip the meal once, it's paid for, and I'm getting better monitoring with less fussing.

But to each their own!
 
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